Electrophotographic liquid developer containing asphalt and modified alkyl resin

ABSTRACT

An electrophotographic liquid developer is provided which comprises a dispersion of at least one coloring material in particle form, asphalt and synthetic resin in an organic solvent having an electrical resistance of no less than 108 Omega . The liquid developer is useful for the preparation of lithographic plates.

0 Waite States Patent 1 [111 3,714,048

Adachi et al. 1 Jan. 30, 1973 1 ELECTROPHOTOGRAPHIC LIQUID Refe encesCited l g gag UNITED STATES PATENTS AND 0 3,554,946 1/1971 Okuno et al..252/62.1 [75] Inventors: Syozo Adachi; Masasi Ueyama, both 3,523,9008/1970 Ueda et al. ..252/62.1

of Tokyo, Ja an 3,438,904 4/1969 Wagner ..252/62.l 3,234,017 2/1966 Heylet al. ..l17/l7.5 [73] Assignee: Iwatsu Electric Company Limited,3,576,744 4/1971 Sharrock et al. ..252/62.l Tokyo, Ja an 3,198,6498/1965 Metcalfe et a1 ..252/62.1 3,058,914 10/1962 Metcalfe et al..252/62.1 [22] Filed: Sept. 28, 1970 [21] Appl. No.: 76,307 PrimaryExaminer--George F. Lesme's Assistant Examiner.l. P. BrammerAtt0rneyRobert E. Burns and Emmanuel J. Lobato [30] Foreign ApplicationPriority Data [57] ABSTRACT Oct. 23,1969 Japan "44/8 1910 An l ph g pdeveloper is p d which comprises a dispersion of at least one coloring[52] U.S. Cl ..252/62.1 material] i parade f asphalt Synthetic resin in[51] Int. Cl. ..G03g 9/04 an rganic olvent having an electricalresistance of no [58] less than 10 0.. The liquid developer is usefulfor the Field of Search ..252/62.1

preparation of lithographic plates.

4 Claims, N0 Drawings ELECTROPHOTOGRAPHIC LIQUID DEVELOPER CONTAININGASPHALT AND MODIFIED ALKYL RESIN This invention relates to anelectrophotgraphic liquid developer, particularly available for thepreparation of lithographic plates.

Heretofore, a liquid developers in electrophotography has only beencontrived for mainly applying them to electrostatic copies andaccordingly, has never been employed in the preparation of so-calledlithographic plate" by which a large number of printed matter whereonhighly images are printed, is produced. Because, in the case whenconventional liquid developer is employed in the process of preparingthe lithographic plate, the following defects are produced; first, adeposited amount of toner constituting images on anelectrophotosensitive paper is less and in many cases, due to so-calledfringing field effect" peculiar to a dry-type electrophotographicprocess, the serious loss of image density in the central part ofhalf-tone images or of the solid area whereon toner should be whollydeposited is caused. Secondly, the weak adhesive power of tonerparticles to the lithographic plates results in poor receptivity ofprinting ink and in diminution of images onprinting because the printedimages cannot withstand the roller pressure produced at the timeprinting.

Generally, in order to obtain good images on a lithographic plate, tonerparticles should have characteristics which satisfy the followingprerequisites;

1. Toner particles should carry a stable positive charge.

2. They should have a microscopic fineness and electricalcharacteristics exhibiting high resolving power.

3. They should be superior in fixation property so that diminution ofthe printed images may be prevented. I

4. They should exhibit good receptivity of printing ink.

5. They should have good abrasion resistance.

6. They should cause less fog formation on the unexposed area.

7. The fringing field effect should appear least and accordingly, goodtone reproduction of the photograph or of the solid area whereon tonerparticles should completely be deposited, is obtainable.

The object of the present invention is to obviate the above-mentioneddefects present in the conventional lithographic processes andaccordingly, to provide an electrophotographic liquid developer usefulfor the preparation of lithographic plates which have thecharacteristics satisfying the above-listed prerequisites.

According to the present invention, there is provided anelectrophotographic liquid developer useful for the preparation oflithographic plates, comprising a uniform dispersion of at least onecoloring material (pigment or dyestuff) in particle form asphalt andsynthetic resin, selected from petroleum resin and oil modifiedsynthetic resin in an organic solvent having an electrical resistance ofno less than lO Qcm, said synthetic resin being at least partiallysoluble in the organic solvent.

The coloring material (dyestuff or pigment) which is used in the liquiddeveloper of the present invention includes not only carbon black, butalso those of various hues, for example, Phthalocyanine Blue, ChromeYellow, Aniline Black, red iron oxide Oil Black, Oil Red and MalachiteGreen because the developer has various uses other than copying. Asdyestuffs, those which are insoluble in a dispersion medium, that is,the organic solvent, are preferable. The particle diameter of thecolorant used in the liquid developer is preferably no more than 10 p.because microscopic particles produce a lithographic plate having ahigher resolving power.

The asphalt which is contained in the liquid developer usually comprisesasphaltene, maltene and oily ingredients.

The synthetic resin which is used in the liquid developer should be atleast partially soluble in the organic solvent mentioned later. Usefulsynthetic resin of this class includes resin and petroleum resin,oilrnodified synthetic resin.

The organic solvents which are used in the liquid developer are thosehaving an electrical resistance of no less than IO Qcm, for example,solvent naphtha, mineral turpentine, turpentine oil, kerosine,n-heptane, carbon tetrachloride, etc. In case the composition ofcoloring material, asphalt and synthetic resin is previously mixed usinga mixer such as a ball mill, it is preferable to employ an organicsolvent containing aromatic hydrocarbon having high dissolving power,for example, solvent naphtha, mineral turpentine or turpentine oil.

The content of the coloring materialmay vary withina range from 5 topercent by weight based on the total solid content in the liquiddeveloper depending upon the particular coloring material and itsphysical and chemical properties the remaining solid material, i.e.asphat and resin, are than present in an amount of 95 to 25 percent byweight.

The content of asphalt also depends upon the particular asphalt and itscharacteristics and may vary within a range from 1 to percent by weightbased on the total solid content other than pigment. However, thecontent of asphalt has relevance to the receptivity of ink and, in viewof the characteristics required as line images on lithographic plate, itis preferable to employ from 1 to 10 percent by weight of asphalt basedon the total solid content. Further, the content of the synthetic resinmay also vary within a range from 10 to 99 percent by weight based onthe total solid content other than pigment depending upon its ratio tothe content of asphalt.

The effects and functions exercised by the above three ingredients inthe liquid developer will be described hereinafter.

The coloring material particles function 'as imageforming elementsin thedeveloper. In view of the fact that the liquid developer of the presentinvention is available for uses other than the usual copying, thedeveloper can be made in any color; the coloring material may includethose of various hues besides carbon black. It is, however, noted thatcontent of both asphalt and synthetic resin should be determined independence of the particular coloring material because coloringmaterials usually have quite different physical and chemical propertiesfrom each other. For example, in the case of the coloring materialhaving a higher oil absorption, the content of both asphalt andsynthetic resin may be increased. On the other hand, if the coloringmaterial has little oil absorption, the content of the asphalt andsynthetic resin should be decreased.

Asphalt is in a massive state composed of associated micelles. Itcomprises asphaltene, maltene and oily materials. It is easily solublein organic solvent mainly containing aromatic hydrocarbon having a highdissolving power, i.e., solvent naphtha, mineral spirit, terpentine oiland the like. Some organic solvents having a high electrical resistancewhich are usually available as diluent, have a lower dissolving powerand therefore, they do not completely dissolve asphalt. However, even inthat case, asphalt forms fine colloidal particles having a high polarityand consequently, exhibits high adsorption together with asphaltmicelles dissolved in the organic solvent. Consequently, the asphalt isadsorbed on the coloring material particles so that charged colloidalparticles composed of coloring material and asphalt are formed. Thecolloidal particles carry positive charges and thusly are repelled byeach other by like charges to produce stable image-forming particles.

Synthetic resin is dissolved in the organic solvent to form a stableorganosol and the organosol is adsorbed as a protective colloid withrespect to the above-mentioned colloidal particle comprising coloringmaterial and asphalt to form stable colloidal particles comprisingcoloring material, asphalt and the synthetic resin.

Some coloring material and the synthetic resin have little wettingproperty or low oil absorption and therefore, the mixture of thecoloring material and the synthetic resin has a tendency to give anunsatisfactory fixation of developed images. But in practice, as asphaltis extremely adsorbent on the coloring material, stable colloidalparticles comprising coloring material, asphalt and the synthetic resinare also obtainable. Thusly formed colloidal particles carrying charges,go hand in hand with protective colloidal action by synthetic resin toprevent the developing agent from aggregating. In other words, becauseasphaltene micelles composing asphalt are extremely adsorbent and carryhigh positive charges, the colloidal particles of coloringmaterial-asphalt-synthetic resin carry positive charges in the aggregateand consequently prevent aggregate-formation between particles.

In view of the fact that the purposes of the synthetic resin used in thepresent invention includes the exertion of a protective colloidal actionon the coloring material-asphalt colloidal particles and the achievementof a satisfactory fixation of developed images, the synthetic resin neednot function as a polarity-controller. Accordingly, the synthetic resinused in the present invention may be chosen from those which are atleast partially soluble and stably dispersible in organic solvent havingan electrical resistance of no less than IO Qcm and which do not reducethe electrical resistance of the organic solvent to that which is lessthan lo flcm. Further, it will be noted that toner particles containingthe synthetic resin should be easily solidified by evaporation oforganic solvent from the toner particles constituting just developedimages or should be spontaneously solidified through oxidativepolymerization of the synthetic resin contained in the toner particles.

One of the most noticeable aspects of the present invention is thatabsence of any one component of the above-mentioned coloringmaterial-asphalt-synthetic resin never answers the purpose of thepresent invention, that is, satisfactory line images on lithographicplate cannot be obtained. For example, in case the developing solutioncontaining only coloring materialasphalt colloidal particles and notcontaining the synthetic resin is employed, line images so formed areeasily destroyed by the roller pressure applied in printing, not tomention mechanical action exerted in development and consequently, theystain the background because physical adsorptive power (fixation) of thetoner particles and frictional resistance are extremely low. On theother hand, in the case of a developing solution containing onlycoloring materialsynthetic resin particles, good images cannot beobtained or, even if better formation of the highly resolved images isexpected, as the adsorptive power of the synthetic resin in the coloringmaterial is inferior to asphalt, line images thusly formed are lackingin receptivity of printing ink. Furthermore, in the case of a developingsolution containing only asphalt-synthetic resin colloidal particles, asno image-forming elements exist the deposited amount of toner on acharged area, on which line images are to be formed, is reduced.Therefore, the above three developers are not suitable for a printingplate.

On the contrary, the developer of the present invention containing theabove three components, obviates the above defects and accordingly, itexhibits excellent stability, good fixation and high resolving power. ltalso exhibits superior reproducibility of all kinds of images such assolid, half tone or thin line and produces good receptiveness ofprinting ink.

The following examples will serve to illustrate the present invention,in which all parts are by weight.

EXAMPLE 1 obtain a developing solution. Using the developing solution,an image was formed on a master paper on which an electrophotosensitivelayer was coated. The resultant lithographic plate was set up on anoffset printing machine after the image-undeveloped area of the printingplate surface was desensitized to oil. 1,000 sheets of printing matterwere printed by the offset machine. Various kinds of printed images,such as photography, large solid area or thin line were extremely clear.

EXAMPLE 2 The following composition, which contained 15 parts ofPhthalocyanine Blue,

10 parts of Oil Black,

5 parts of blown asphalt having a hardness scale (penetration of theindentor) of 30 40,

40 parts of vinyltoluene oil containing 40 percent of vinyltoluene; and

30 parts of n-heptane was mixed and dispersed for 20 hours in a ballmill and then, the resultant dispersion was charged into 30 l ofn-heptane with stirring to obtain a developing solution. Using thedeveloping solution, a lithographic plate was prepared and 5,000 sheetsof printing matter were printed in the same manner as described inExample 1. Various kinds of printed images, such as photography, largesolid area or thin line exhibited good tone reproduction and excellentclearness.

EXAMPLE 3 A following composition, which contained 20 parts of MalachiteGreen,

parts of straight asphalt having a hardness scale (penetration of theindentor) of 100 120,

40 parts of terpene resin; and

'30 parts of carbon tetrachloride was mixed and dispersed in a ball millfor hours and then, the resultant dispersion was diluted with l ofkerosine to obtain a developing solution. Using the developing solution,lithographic plates were prepared and 3,000 sheets or printing matterwere printed as described in the above Examples. The printed images wereclear as described above.

' What we claim is:

1. An electrophotographic liquid developer for the preparation oflithographic plates which comprises a uniform dispersion of at least onecoloring material in particle form having an average particle diameterof no more than 10 microns selected from pigment and dyestuff capable ofcarrying a positive charge, asphalt and an oil modified alkyd resin, inan organic solvent having an electrical resistance of no less than 10 0cm., said resin being at least partially soluble and not reducing theelectrical resistance of said solvent to less than 10 0. cm., saiddispersion containing 5 to percent by weight of said coloring materialbased on the total weight of solid material and in the remaining solidmaterial of said dispersion, said oil-modified alkyd resin being presentin an amount of 10 'to 99 percent by weight and said asphalt in anamount of l to percent by weight based on the amount of said asphalt andresin in said dispersion.

2 An electrophotographic liquid developer according to claim 1 whereinsaid coloring material is insoluble in said organic solvent.

3. An electrophotographic liquid developer according to claim 1 in whichsaid organic solvent contains aromatic hydrocarbon.

4. An electrophotographic liquid developer according to claim 1 in whichsaid oil-modified alkyd resin is a soybean oil-alkyd resin.

1. An electrophotographic liquid developer for the preparation oflithographic plates which comprises a uniform dispersion of at least onecoloring material in particle form having an average particle diameterof no more than 10 microns selected from pigment and dyestuff capable ofcarrying a positive charge, asphalt and an oil modified alkyd resin, inan organic solvent having an electrical resistance of no less than 108Omega cm., said resin being at least partially soluble and not reducingthe electrical resistance of said solvent to less than 108 Omega cm.,said dispersion containing 5 to 75 percent by weight of said coloringmaterial based on the total weight of solid material and in theremaining solid material of said dispersion, said oil-modified alkydresin being present in an amount of 10 to 99 percent by weight and saidasphalt in an amount of 1 to 90 percent by weight based on the amount ofsaid asphalt and resin in said dispersion.
 2. An electrophotographicliquid developer according to claim 1 wherein said coloring material isinsoluble in said organic solvent.
 3. An electrophotographic liquiddeveloper according to claim 1 in which said organic solvent containsaromatic hydrocarbon.